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SQL Server 2000 Stored Procedure Programming
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If @intErrorCode = 0 and @insOrgUnitId is not null Begin set @chvWhere = @chvWhere + ' OrgUnitId = ' + @insOrgUnitId + ' AND' Select @intErrorCode = @@Error End If @intErrorCode = 0 and @chvUserName is not null Begin set @chvWhere = @chvWhere + ' UserName = "' + @chvUserName + '"' Select @intErrorCode = @@Error End if @debug <> 0 select @chvWhere chvWhere -- remove ' AND' from the end of string If @intErrorCode = 0 And Substring(@chvWhere, Len(@chvWhere) - 3, 4) = ' AND' Begin set @chvWhere = Substring(@chvWhere, 1, Len(@chvWhere) - 3) Select @intErrorCode = @@Error if @debug <> 0 select @chvWhere chvWhere End If @intErrorCode = 0 and Len(@chvWhere) > 0 Begin set End if @debug <> 0 select @chvQuery Query -- get contacts If @intErrorCode = 0 Begin exec (@chvQuery) Select @intErrorCode = @@Error End return @intErrorCode @chvQuery = @chvQuery + ' WHERE ' + @chvWhere Select @intErrorCode = @@Error
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Advanced Stored Procedure Programming
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To avoid problems with the mixing of single and double quotes, I used the Set Quoted_Identifier Off statement at the beginning of the query. Figure 10-1 shows the result of the stored procedure (along with some debugging information).
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Using the sp_executesql Stored Procedure
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In 3, we saw that an important advantage stored procedures have over ad hoc queries is their capability to reuse an execution plan. SQL Server, and developers working in it, can use two methods to improve the reuse of queries that are not designed as stored procedures. The first of these is autoparameterization, which we
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The results of Query By Form
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SQL Server 2000 Stored Procedure Programming
covered in 3. Now we will focus on using a stored procedure to enforce parameterization of a query. If a developer knows that a query will be reexecuted with different parameters and that reuse of its execution plan will not degrade performance, he or she can use sp_executesql to run it. This stored procedure has the following syntax:
sp_executesql [@stmt =] stmt [ {, [@params =] N'@parameter_name data_type [,...n]' } {, [@param1 =] 'value1' [,...n] } ]
The first parameter is a string with a batch of Transact-SQL statements. If the batch uses parameters, the developer must also supply their definitions as the second parameter of the procedure. The definition is followed by a list of parameters and their values. The following script executes one batch twice using different parameters:
EXECUTE sp_executesql @Stmt = N'SELECT * FROM Asset.dbo.Contact WHERE ContactId = @Id', @Parms = N'@Id int', @Id = 11 EXECUTE sp_executesql @Stmt = N'SELECT * FROM Asset.dbo.Contact WHERE ContactId = @Id', @Parms = N'@Id int', @Id = 313
There is one unpleasant requirement to this exercise. If all database objects are not fully qualified (that is, hard-coded with the database name and object owner), the SQL Server engine will not reuse the execution plan. In some cases, you may be able to ensure that all database objects are fully qualified. However, this requirement will become a problem if you are building a database that will be deployed under a different name or even if you use more than one instance of the database in your development environment (for example, one instance for development and one for testing).
10:
Advanced Stored Procedure Programming
The solution is to obtain the name of a current database using the DB_NAME function. You can then incorporate it in a query:
Declare @chvQuery nvarchar(200) Set @chvQuery = N'Select * From ' + DB_NAME() + N'.dbo.Contact Where ContactId = @Id' EXECUTE sp_executesql @stmt = @chvQuery, @Parms = N'@Id int', @Id = 1 EXECUTE sp_executesql @stmt = @chvQuery, @Parms = N'@Id int', @Id = 313
Solutions based on this stored procedure are better than solutions based on the execution of a character string. The latter are not reused very often. It might happen that they will be reused only when parameter values also match. Even in a situation where we are changing the structure of a query, there are a finite number of possible combinations of query parameters (and some of them are more probable then others). Therefore, reuse will be much more frequent if you force parameterization using sp_executesql. When you use Execute, the complete batch has to be assembled in the form of a string each time. This requirement also takes time. If you are using sp_executesql, the batch will be assembled only the first time. All subsequent executions can use the same string and supply an additional set of parameters. Parameters that are passed to sp_executesql do not have to be converted to characters. That time is wasted when you are using Execute. By using them in their native format in sp_executesql, you may be able to detect errors more easily.
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